1. Field of the Invention
The present invention relates generally to an improved hydronic heater, and particularly to a modulating hydronic heater of compact size and high efficiency.
2. Prior Art
Central heating systems employing hot water circulating through a network of pipes have been used for many years for room space heating, snow melting, indirect swimming pool heating, and other similar purposes. Such systems are now generically referred to as hydronic heating systems.
Much of the prior art relating to hydronic heaters is concerned with the design or regulation of an integrated heating system such as could be used to heat open space and to supply hot water for domestic use. Thus, U.S. Pat. No. 3,171,387, entitled "Combined Heating and Warm Water Preparing Apparatus" teaches an apparatus for efficiently providing heated water for space heating or domestic use regardless of environmental temperature. U.S. Pat. No. 3,341,122, entitled "Integrated Hydronic Heating System" teaches a similar apparatus. U.S. Pat. No. 4,178,907 entitled "Unified Hot Water and Forced Air Heating System", teaches an apparatus which uses air for space heating while providing hot water for domestic use.
Hydronic heaters of the prior art have typically been large. Attempts to reduce the size of such heaters has led to inefficiency. Hydronic heaters typically have a gas-to-water heat exchange chamber in which hot combustion gases from a combustion chamber flow over tubing containing water to be heated. Because of low gas velocities and associated heat transfer coefficients, large surface areas are required to achieve good heat transfer. To make a more compact unit and still maintain good heat transfer, finned tubing is used to transfer heat from the hot gases to the circulating water.